The aim of the invention is essentially to propose a solution for obtaining, from a relatively simple light device of the elliptical type, various light beams corresponding to various cutoff lines satisfying various standards and/or regulations, in particular without having recourse to a multitude of shields.
The field of the invention is, in general terms, that of lighting devices of the motor vehicle light type. In this field, various types of light device are known, amongst which there are essentially:                side lights, with low intensity and range;        passing, or dipped-beam, lights, with greater intensity and range on the road of around 70 metres, which are used essentially at night and where the distribution of the light beam is such that it makes it possible not to dazzle the driver of a passing vehicle;        long-range headlights, and auxiliary lights of the long range type, where the area of vision on the road is around 200 metres, and which must be switched off when passing another vehicle in order not to dazzle its driver;        fog lights.        
In addition, a type of improved light is known, referred to as dual-function lights, which combine the functions of dipped lights and long-range lights: for this purpose, it is possible for example to dispose inside the dual-function light a removable shield consisting for example of a metallic plate, able to move on demand from a first position in which it does not obscure the light beam produced by the light source of the light, the range of the light then corresponding to that of main-beam lights, and a second position in which it obscures part of the light beam produced by the light source of the light, the range of the light then being limited to that of dipped lights. The light must, in the second position, generate a beam with a regulatory cutoff corresponding to a dipped beam, the form of the cutoff being given by the form of the shield intercepting part of the light beam. This type of design is principally used in light devices of the elliptical type.
However, the conventional light devices which have just been mentioned, more particularly those which are used as dipped lights, produce light beams which are open to improvement when these light devices are used in certain conditions.
Thus, when a vehicle is on a motorway, it is judicious to concentrate the light flux of the dipped light at the optical axis of the light device, in order to make the beam produced carry a little further. On the contrary, when a vehicle is travelling in town, it is not necessary to make the light beam carry as far as on clear roads.
Thus, in addition to the conventional main light functions, in particular dipped and main beam, various improvements have progressively appeared. Thus elaborate functions or advanced functions have been seen to develop which slightly modify the positioning of the cutoff of the light beam produced, amongst which there are in particular:                a function known as Town Light in English, standing for town beam. This function provides a slight reduction in the range of the light device, possibly by providing a broadening of the beam of the dipped beam type;        a function known as Motorway Light in English, standing for motorway light. This function provides an increase in the range of a dipped light.        
In addition, it must be recalled that, for countries where the traffic travels on the right, the cutoff line of a beam of the dipped type is symmetrical, with respect to a vertical central axis, with that observed in countries where the traffic travels on the left. FIG. 1 depicts, by way of example and schematically, four projections on a planar surface of the various light beams that have just been mentioned. The planar projection surface is disposed facing the light device in question, perpendicular to its optical axis. The darkened part of these projections corresponds to an absence of light in this part, the part left white corresponding to a normal illumination by means of the light device in question. Thus there have been shown a first cutoff 101, corresponding to a dipped beam in traffic on the right, a second cutoff 102 corresponding to a motorway beam in traffic on the right, a third cutoff 103 corresponding to a town beam or fog light, a fourth cutoff 104 corresponding to a dipped beam in traffic on the left, a fifth cutoff 105 corresponding to a motorway beam in traffic on the left and a sixth cutoff 106 corresponding to a main beam.
It is therefore sought to propose light devices which are capable of modifying the cutoff of the light beam that they produce, so as to be able to propose alternatively in particular the six beams shown in FIG. 1.
To this end various solutions have been proposed in the prior art.
A first solution, described in the document U.S. Pat. No. 5,673,990, consists of a light device provided with a movable screen for in particular vertical sliding in order to form on demand a beam with a particular cutoff.
A second solution, described in the European patent application EP 1 197 387, describes the use, in each light device of the dipped beam type, of a plate, approximately square in shape, in rotation on itself, the axis of rotation being inclined with respect to a main lighting axis. Each side of the plate makes it possible to obtain a light beam corresponding to a particular cutoff when the side in question is brought, by rotation of the plate, facing the light source of the light device in question.
However, with these two solutions, the changes in position of the screens or movable plates in order to pass from a first beam having a first cutoff to a second beam having a second cutoff take place by means of awkward transition phases with a modification disturbing the light distribution below the cutoff line. Moreover, the first solution requires a particularly complex and high-precision mechanism.
One object of the invention is to respond to all the problems that have just been mentioned. To this end, in the invention, it is proposed to use a shield rotationally moving about a substantially vertical axis, or one inclined with respect to the vertical. Part of the shield terminates in a so-called “active” edge (that is to say the edge which will determine the light/dark limit of the light beam emerging from the light), the shape of which defines the cutoff of the beam of the light device in which the shield is disposed. It is a case generally of the top edge of the shield, “top” having to be understood in the light of the shield mounted in the light in the operating position in the vehicle. In order to be able to offer a large number of distinct cutoffs by means of the same shield moving in rotation, it is proposed, in the invention, that certain sectors of the “active” top part of the shield make their contribution in the production of several cutoffs.
To this end, in the invention, a clever succession of shapes is proposed, defining the active or top edge terminating the shield, so that at least part of one of these shapes can be used in the production of at least two beams, having different cutoffs, preferably corresponding to two consecutive positions of the shield considering the rotation movement of the shield about the vertical axis.